This invention relates to an apparatus and method for separating gas and solid particles from well fluids, and more particularly to such an apparatus and method in which a separator imparts a helical motion to the gas and solids for separating the gas and solids from a liquid well fluid which is pumped to a surface location.
A pumping well is normally equipped with a string of casing, a string of tubing depending within the casing, a pump attached to the lower end of the tubing string and a gas anchor attached to the pump over the suction inlet of the pump. Oil flowing into the bottom of a well often contains large quantities of gas which, unless separated from the oil, are drawn into the pump. The displacement capacity devoted to the compression of this gas in a pump reduces its liquid capacity. Also, the power required to compress any free gas entrained with the oil drawn into an oil well pump is largely wasted. It is therefore necessary, insofar as practical, to exclude the entry of gas from the pump in order to minimize the size and initial cost of the pumping system as well as the operating and maintenance costs.
In liquid producing wells and particularly in deep producing wells where liquid is pumped to the surface, a problem is often encountered handling the gas commonly associated with the liquid in the producing formation. There is usually a substantial decrease in pressure on the liquid-gas mixture as it moves out of the liquid-bearing formation into the production well. Hydrocarbon gas, either in solution with the liquid or in the free state, expands as the gas-liquid mixture enters the production borehole. If the gas is pumped with the liquid to the surface serious difficulty is likely to be encountered with the pumping apparatus. A positive displacement pump will act as a compressor of the gas and will lose much of its efficiency in lifting liquid to the surface. In severe cases, the pump may become xe2x80x9cgas lockedxe2x80x9d as a result of pumping gas and damage to the pump may result.
Gas and liquid separators have been utilized in order to remedy this problem. Generally, the gas and liquid separator is a device which, by utilizing the different properties of the two substances, affects the separation of the liquid which is usually a mixture of oil and water and the gas and allows them to be moved to the surface through different conduits. It should be noted, however, that separators are useful not only to separate well liquids and gas, but may also be used in separating any two fluid substances which have different specific gravities. An example of a separator other than gas and well liquid separators where the apparatus may be used effectively includes a separator for separating a gas and water mixture. Therefore, the separator described herein as primarily useful as a gas and well fluids separator, may be used to perform similar operations with no substantial alteration of the apparatus itself such as a water well.
A typical device for separating liquid and gas uses centrifugal force to assist in separating the gas form the liquid and provides an arrangement of conduits for transmitting the gas and liquid to the surface. There is still need, however, for a more efficient gas-liquid separator which utilizes centrifugal force in assisting the separation of the liquid and gas and provides a more direct and easy passage of the liquid and gas to the surface thus resulting in less pressure drop in the separator and also simpler construction.
In the production of liquid hydrocarbons from wells which are not free flowing it is common practice to use electric motor driven submersible pumps or similar type pumps with downhole motors for pumping the liquid to a surface location through a pipe string. One problem associated with the use of downhole motor driven pumps, in particular, is that the liquid being pumped can have only a limited amount of gas entrained therein without developing overheating or other operating problems which may damage the pump and generally cause unsatisfactory operation. Typically the entrained gas in the pump inlet fluid flow stream should not exceed about 15 percent by volume for best results.
Gas-liquid separators or so-called gas anchors have also been developed for downhole well pumps which force the gas-liquid mixture to undergo spiral or helical flow to effect separation of the gas and liquid due to centrifugal forces acting thereon. Various arrangements of gas-liquid separators which effect a somewhat spiral or helical motion to the fluid mixture to effect separation of gas and liquids have been used heretofore.
U.S. Pat. No. Re 35,454 reissued Feb. 18, 1997 shows an apparatus and method in which gas and solids are separated from liquids in the well fluids. A separator is provided in a tubing string below a downhole pump and spiral guide means impart a helical motion so that solid particles particularly settle downwardly. An embodiment shows particularly in FIG. 5 includes a gas separator in which gas is removed from the well fluids through vertical slots and is directed upwardly in an annulus between the spiral guide means and the inner tubular housing receiving the clean liquid after the gas has been removed from the well fluids. The separated gas is directed upwardly to a surface location through a check valve. However, with a high velocity fluid flow, a substantial amount of the gas does not enter the slots and remains with the liquid for entering the pump.
It is desired that an improved separator device be provided for the effective separating of gas and solids from well fluids for the upward flow of a clean liquid after the gas and solids have been removed.
The present invention is particularly directed to a downhole separator device on the end of a pipe string in a borehole which is effective to remove gas and solids from the well fluid so that a clean liquid product is directed upwardly to a surface location after removal of gas and solids from the well fluid. While the well fluid may be a fluid containing hydrocarbons, the well fluid may be water and the present apparatus and method is effective for water as well as hydrocarbons.
The downhole separator of the present invention is positioned on the end of a pipe string and lowered within an outer casing of a bore hole for separation of gas and solids from the well fluid. The downhole separator includes an outer tubular housing having openings therein to receive the well fluid from the annulus between the outer casing and the outer tubular housing of the separator. An inner concentric flow tube has an open lower end for the upward flow to a surface location of the clean liquid from the well fluid after gas and solids have been removed. The pipe string normally comprises production tubing and the clean liquid may be pumped upwardly through the production tubing string.
The gas and solids are removed from the well fluids in two separate steps by two separate spirals, one spiral for the gas and a separate spiral for the solids. An upper gas spiral is positioned below the openings in the outer tubular housing and a separate lower spiral spaced axially from the upper gas spiral is provided for the solids. The spirals are positioned in the annulus between the outer tubular housing and the inner flow tube. The spirals provides a helical flow and are spaced axially from each other a distance, for example, of about four (4) inches to create a swirl chamber therebetween in which the separated gas then flows upwardly normally in the outer annulus between the outer tubular housing and the casing. The gas accumulates in the swirl chamber between the spirals and is liberated from the liquid. The gas normally exists as large bubbles almost filling the area and is separated by slugs of liquid. Thus, the liquid flows downwardly in a helical path to the solids spiral.
A gas spiral housing is mounted in the annulus between the outer tubular housing and the flow tube and has spiral guides or guide members mounted on the lower end for directing the well fluid downwardly. An inner gas annulus is defined between the inner peripheral surface of the gas spiral housing and the outer peripheral surface of the inner flow tube to receive the upward flow of gas from the swirl chamber below the upper gas spiral and above the lower axially spaced solids spiral. A relatively large capacity gas reservoir is provided adjacent the upper end of the inner gas annulus to receive the separated gas therefrom. A suitable discharge control member, such as a check valve or orifice, for example, may control the flow of liquid into the gas reservoir from the annulus between the casing and the outer tubular housing of the separator.
The solids, such as sand or iron sulfide, for example, are separated from the well fluid by the solids spiral and fall by gravity into a mud anchor or other suitable collection area. The liquid then flows upwardly in the flow tube to be pumped for flow to a surface location.
An embodiment of the invention is particularly directed to a separator utilized with a downhole motor driven pump. A shroud or outer housing is provided about the motor and pump inlet so that clean liquid fluid from the separator is discharged below the motor from the pipe string and then flows upwardly within the housing about the motor for cooling the motor. The liquid after cooling the motor enters the intake for the pump for flow through the pipe string to a surface location.
It is an object of the invention to provide a downhole separator in a bore hole effective for the removal of gas and solids in separate steps in a well fluid.
A further object of the invention is to provide such a separator having separate axially spaced gas and solid spirals for the separation of gas and solids from well fluid to provide a clean liquid for upward flow to a surface location.
Another object of the invention is to provide a gas and solid""s separator on the end of a production tubing in a production oil well for the separation of gas and solids from the hydrocarbon well fluid for upward flow of liquid oil in the production tubing.
A further object of the invention is to provide such a separator having a gas spiral within multiple guide members for gas and a solids spiral preferably with multiple guide members for solids to provide a relatively short length compact separator.
Another object of this invention is the provision of a shroud about the downhole motor and pump inlet to effect circulation of upwardly flowing clean liquid about the motor for cooling the motor.
An additional object of the invention is the provision of a relatively long large capacity gas reservoir above the gas spiral for the storage of separated gas therein for discharge to a surface location when the gas reaches the required pressure in the gas reservoir for return to the casing annulus.
Other objects, features, and advantages of the invention will be apparent from the following specification and drawings.